The invention relates to ventilation system for synchronous electrical machines, such as generators and motors. In particular, the invention relates to a stator mounted cooling fan for a forced gas stator ventilation system for generators having superconducting rotors.
In the process of producing electricity, power generators create heat that must be dissipated from the generator. Heat occurs in generators due primarily to windage and friction, electric current flow, and time-varying magnetic fields in magnetic structures. Frictional heating occurs as the rotor spins at high speed in the generator. Heating also occurs as current flows through the rotor and stator coils, as they rotate relative to one another in the magnetic fields of the generator. Losses in the magnetic circuit occur as the magnetic fields change with time in permeable materials, such as for example in the stator core and the rotor poles of a synchronous generator.
Generators are conventionally equipped with cooling systems, such as a gas ventilation system, to transfer heat from the stator and rotor away from the generator. Gas ventilation cooling systems have been used in conventional generators and motors that do not employ superconducting coils. These generators and motors have stators and rotors that require cooling. The conventional gas ventilation systems tightly couple the cooling of stator and rotor by providing cooling gas to both. The ventilation system cools the rotor and stator by forcing cooling gas through gas passages in the rotor and stator. Conventional ventilation systems have employed forward flow and reverse flows of cooling gases through the stator and rotor.
In a forward flow ventilation scheme the cooling gas flows through the rotor and stator. The rotor expels cooling gas into the air gap, where the expelled rotor flow mixes with “fresh” gas. The “fresh” gas flows from the fan and moves axially through the air gap along the length of the machine. The combination of the “fresh” gas and expelled rotor flow, flow into the stator cooling passages and serve to cool the stator. In a reverse flow ventilation scheme the rotor expels cooling gas into the air gap, where the expelled rotor flow mixes with gas which is expelled from the stator cooling passages. The combined flow then moves axially along the length of the machine and exits through the fan. Both forward flow and reverse flow ventilation schemes tend to couple the cooling of rotor and stator.
Because of the coupling of the cooling gas flows through the rotor and stator, conventional forward and reverse flow ventilation systems are configured to provide adequate cooling for both the stator and rotor. To cool the rotor, some compromises may have to be made in a conventional ventilation system with respect to cooling the stator in order to accommodate cooling needs of the rotor, and vice versa. It may be difficult to optimize the cooling of the stator or rotor with a ventilation system that must provide cooling for both the rotor and stator. Nevertheless, ventilation systems have conventionally provided cooling for both the stator and rotor in large industrial and utility power generators.
The cryogenic cooling system for a superconducting rotor does not cool the stator. The stator of such a superconducting synchronous machine requires a separate stator cooling system. Contrary to conventional machines where stator and rotor cooling systems are coupled in a single ventilation system, the cooling system of the cryogenic rotor and the gas-cooled stator may be separate and independent.